The fiber-reinforced polymers (FRP) bar is a promising solution to problems caused by steel rebar corrosion in concrete. To assess the service life of the FRP bar based on accelerated test results, it is crucial to have a reliable model. Here, a modified exponential (MEP) model is proposed based on the Avrami equation. The Avrami equation provides a theoretical foundation for the empirical exponential (EP) model and does not a priori fix the power of the exposure time to one. A database containing 903 data points from 74 groups of test specimens is assembled to compare the reliability of the MEP model vis-a-vis the EP, single logarithmic, double logarithmic, and power function models. The combination of Root Mean Square Error (RMSE), the Mean Absolute Error (MAE), and the coefficient of determination (R2) criteria is proposed for assessing model reliability. It is shown that in certain cases the combined criteria, versus R2 alone, significantly increase the number of test groups meeting the acceptable performance limit. Observed test data aberrations are found to have minor influence on the results of the EP model, but they significantly influence the results of the other four models. The EP model generally predicts the lowest activation energy and the smallest strength retention for similar groups of bars, while the predicted values of the other four models exhibit a relatively small difference. The difference between the predicted strength retention values of the EP and MEP models shows an increasing trend with the increase of the absolute value of (1 − n), where n is the power of the exposure time in the MEP model.
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In this study, the dynamic response of typical wide-flange steel beams was experimentally evaluated under blast loading. A total of 13 beams were field tested using live explosives, where the charge size ranged from 50 to 250 kg of ammonium nitrate-fuel oil mixture, and the ground stand-off distance was from 7.0 to 10.3 m. Blast wave characteristics, including incident and reflected pressures, were recorded. In addition, time-dependent displacements, accelerations, and strains at different locations along the steel members were measured, and the postblast damage and mode of failure of the test specimens were observed. The blast load characteristics were compared with those obtained using the Technical Manual UFC 3-340-02 results. The displacement response results were used to validate the results obtained from a nonlinear dynamic analysis based on a single degree-of-freedom (SDOF) model. Results showed that the UFC 3-340-02 pressure predictions compare reasonably well with the measured pressure in the positive phase in terms of both the peak pressure and overall time variations. The SDOF model predicted the maximum displacements of beams in the elastic range reasonably well, but it overestimated them in the plastic range.
The increasing tendency to use urban civilian buildings for military purposes prompts the need for the assessment of their blast resistance. Many of these buildings are made of reinforced concrete (RC). Popular tools available for the assessment of existing RC structures in practice include guidelines and design standards, technical manuals and specialised software. These tools include certain assumptions based on scarcely available test data, as historically they were collected for military purposes. Efforts to transfer this knowledge from military to civilian applications are relatively recent and need be corroborated by further testing and numerical analysis. The objective of this paper is to present the results of field tests on full-scale RC members to check the validity of a number of assumptions routinely made in current numerical/analytical models. The data captured during the tests, including reflected pressure and member displacements, are compared with results of empirical and numerical models, in order to gauge the robustness and accuracy of the assumptions underpinning these models. Finally, recommendations are made for an expedient assessment of existing buildings based on simple methodologies.
Premature debonding of externally bonded FRP laminate from retrofitted reinforced concrete (RC) members can lead to inefficient use of FRP and can limit the level of strength increase that can be achieved. In this investigation, π-CFRP anchors are used in an attempt to delay the onset of premature debonding and to achieve higher strength in beams retrofitted with a 1.2 mm thick and 50 mm wide CFRP laminate. This investigation consisted of testing six large scale T-beams with a 4500 mm span, 400 mm height and 500 mm flange width under four-point bending. Two beams were tested without retrofit as control beams, one beam with the laminate epoxy bonded to the beam and the remaining three beams with the laminate epoxy bonded and anchored using CFRP π-anchors. One of the beams with 30 anchors exhibited a 46% increase in the debonding load over the beam without anchors while the laminate attained a maximum strain equal to 80% of its ultimate strain capacity, a 94% increase compared to the maximum strain reached in the companion beam strengthened with only the epoxy bonded laminate. The displacement ductility ratio of the latter beam at debonding exceeded 4. The results demonstrate the π-anchoring system effectiveness and a feasible way for efficiently utilizing strong and thick laminates in strengthening RC members.
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The rigid‐ice model of frost heave is one of the most comprehensive frost‐heave models but is restricted to one‐dimensional cases in its present form. In this paper, the model is extended to two‐dimensional problems. The complete formulation of the partial differential equations governing heat, moisture and ice transport in freezing soils is provided. The equations are subsequently solved using the Galerkin finite element method in space and the finite difference method in time. A computer program is developed for the two‐dimensional rigid‐ice model. A case of freezing around chilled gas pipeline is solved and the numerical results are compared with experimental values, with good agreement between the two sets of results.
PCM Trombe walls have been an effective passive technology to achieve energy efficiency. However, the majority of previous research investigated the PCM Trombe walls primarily focused on structural improvement, and very few studies have focused on mixed-dry climate Therefore, in this study, ten scenarios were created and simulated by the validated CFD model under a mixed dry climate. The findings indicate that in summer, an external PCM layer with a melting point of 38 °C could reduce the maximum peak load by 48.9 %, decrease the fluctuation amplitude by 76 %, reduce the cooling load by 14.4 %, compared to the reference case, and yields time lags of 4.5 h and 6.1 h for the maximum and minimum indoor temperatures, respectively. In winter, an external PCM layer with a melting point of 30 °C can reduce the thermal load by 38.2 %, decrease the fluctuation amplitude by 28.5 %, compared to the reference case, and achieve time lags of 4.0 h and 1.7 h for the minimal and maximum indoor temperatures, respectively. Overall, the PCM layer should be placed adjacent to the air channel, and the appropriate PCM melting points in summer and winter are different.
Shrinkage cracking is one of the factors that cause deterioration of reinforced concrete structures. The cracks facilitate the ingress of moisture, oxygen and chlorides to the steel reinforcement surface, which results in steel corrosion and subsequent deterioration of the structure. In this paper, a field investigation was conducted and a monitoring program was designed and implemented to evaluate the performance of the polymer grid in controlling shrinkage cracking under realistic conditions. The monitoring program extended for a period of three years. At the end of the three years period, some samples were cored from the cracked sections and transferred to the laboratory to measure the variation of crack width through the depth and the residual tensile strength of the partially cracked cores. The results show that the polymer grid reduced both the width and density of shrinkage cracks, and endowed partially cracked concrete with higher residual tensile strength. Also, limited and preliminary data indicate that the grid reduced the permeation of chlorides from deicing salt.
The flanges of T- and I-beams are subjected, near their junctions with the web, to three in-plane forces: N x , N y , and N xy , where x and y are horizontal axes parallel and normal to the beam axis. The finite element method is used to study the variation of these forces in T-beams under point or line load. It is concluded that forces N x and N xy can be determined for design purposes using conventional engineering beam theory. Force N y , on the other hand, cannot be determined by available closed-form solutions. Based on a detailed parametric study, a simplified procedure is proposed for determining N y . Key words: beams (supports), connections, finite element, flanges, loads (forces), T-beams, webs (supports).
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